Updated mediawiki/extensions
Project: mediawiki/extensions/CirrusSearch  d721e5dbcae3ed63e8de26b1d51e5863728bb5c0

Clean up test documentation

Add pointer to testing README in main README
Add link to mediawiki-selenium documentation in testing README
Fix some formatting in testing README

Change-Id: I71634532bcdb25bc2e5a0bc549e1fac30976650f